Measured as a Share of the Economy, the Size of the Trade

Measured as a share of the economy, the size of the trade sector (exports plus imports) of the United States has

A) been increasing since 1980, but it declined during 1960-1980.
B) been relatively constant during the last four decades.
C) increased by about 10 percent during the last four decades.
D) approximately doubled since 1980 and tripled since 1960.